In article ,
Andy Hall wrote:
Think a gravity system is where the hot water circuit isn't pumped. If
you've got motorised valves etc, it probably is.

You can have a C plan set up where the boiler/DHW cylinder circuit is
gravity (meaning convection) and a zone valve and thermostat are used
to prevent the hot water from overheating.

Hence my use of 'probably'. I'm sure it's possible, but I've never seen it.

More common was a sort of TRV to control the water temperature, rather
than just the boiler stat.

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*Why is the third hand on the watch called a second hand?

Dave Plowman London SW 12
RIP Acorn